Self-crosslinking vinyl acetate latices

ABSTRACT

AN AQUEOUS LATEX OF A VINYL ESTER POLYMER IS DESSCRIBED WHICH HAS THE PROPERTY OF FORMING SELF-CURING FILMS WITHOUT THE USE OF AN EXTRANEOUS CURING ADDITIVE. THE LATEX IS USEFUL AS A BINDER, PARTICULARLY FOR NON-WOVEN FIBRES, OR FOR WOOD PANEL COATING OR TEXTILE COATING. THE POLYMER COMPRISES A MAJOR PROPORTION OF AVINYL ESTER MONOMER, TYPICALLY VINYL ACETATE, WHICH IS INTERPOLYMERIZED WITH POLYMERIZABLE COMONOMERS COMPRISING A FILM-FORMINGTEMPERATURE REGULATING AMOUNT OF A COMONOMER, TYPICALLY AN ACRYLATE ESTER, A MINOR AMOUNT OF CROSS-LINKING REACTIVE COMONOMERS, TYPICALLY N-METHYLOLCRYLAMIDE AND A CURE CATALYZING AMOUNT OF AN ETHYLENICALLY MONO-UNSATURATED CARBOXYLIC ACID SUCH AS ACRYLIC ACID. IN A PREFERRED EMBODIMENT, A MINOR AMOUNT OF A SYUNERGISTIC, SECOND CROSS-LINKING AGENT IS USED AS DIALLYL MALEATE. THE POLYMER IS DISPERSED IN AN AQUEOUS EMULSION USING AN ANIONIC OR NONIONIC SURFACTANT OR MIXTURES THEREOF, TYPICALLY A MIXTURE OF AN ALKARYL POLYETHER ALCOHOL AND AN ALKALI METAL SULFOSUCCINATE HALF ESTER OF AN ETHOXYLATED ALCOHOL.

United States Patent cc 3,714,096 SELF-CROSSLINKING VINYL ACETATE LATICES Giovanni Biale, Placentia, Calif., assignor to Union Oil Company of California, Los Angeles, Calif. No Drawing. Filed Sept. 3, 1970, Ser. No. 69,478

Int. Cl. C08g 51/24; C09d /02 US. Cl. 260-29.4 UA 19 Claims ABSTRACT OF THE DISCLOSURE An aqueous latex of a vinyl ester polymer is described which has the property of forming self-curing films Without the use of an extraneous curing additive. The latex is useful as a binder, particularly for non-woven fibers, or for Wood panel coating or textile coating. The polymer comprises a major proportion of a vinyl ester monomer, typically vinyl acetate, which is interpolymerized with polymerizable comonomers comprising a film-form1ngtemperature regulating amount of a comonomer, typically an acrylate ester, a minor amount of cross-linking reactive comonomers, typically N-methylolcrylamide and a cure catalyzing amount of an ethylenically mono-unsaturated carboxylic acid such as acrylic acid. \In a preferred embodiment, a minor amount of a synergistic, second cross-linking agent is used such as diallyl m'aleate. The polymer is dispersed in an aqueous emulsion using an anionic or nonionic surfactant or mixtures thereof, typically a mixture of an alkaryl polyether alcohol and an alkali metal sulfosuccinate halrf ester of an ethoxylated alcohol.

DESCRIPTION OF THE INVENTION This invention relates to emulsions of cross-linking vinyl ester interpolymers and, in particular, relates to such interpolymers which are capable of forming films having self curing properties.

Aqueous dispersions of polymers have found increasing acceptance for use in textile and wood panel coating, as well as a binder for non-woven fibers, e.g., polyester fiber fills. In addition, the aqueous dispersions of such polymers have been used for sizing in the textile industry.

Acceptable latexes or dispersions of these polymers must possess a diversity of properties. Such compositions should form films which are cross-linkable into a highly insoluble resin coating, the resultant film should resist discoloration, have a high degree of clarity and be resilient and compressible. The latex compositions should be stable emulsions of the polymer in Water and should have a sutficient viscosity and surface tension to permit spray application of the latex. After application, the polymer should cure rapidly and completely in a short time and at a low temperature so as to be satisfactory under most or all of a wide variety of curing conditions. Preferably, the polymer film should be self-curing to avoid the necessity for use of an extraneous catalyst.

Latexes of acrylic polymers have been used in the past for this application since such polymers have been found to possess a high degree of most of the foregoing properties. Acrylic monomers, however, are relatively expensive and a distinct advantage could be achieved if the less expensive vinyl ester monomers could be substituted as the major component of such polymers. These vinyl esters, and in particular vinyl acetate, offer a distinct cost advantage over acrylics; however, difficulty has been experienced in achieving stable emulsions of vinyl ester polymers which contain suificient cross-linking additives to attain the desired curing response. Prior latexes have also generally required the use of a curing agent, generally an acid or acidic salt, and have thus possessed a limited 3,7M,% Patented Jan. 30, 1973 shelf life or required pre-application addition of the curing agent.

An object of this invention, therefore, is to provide a vinyl ester interpolymer which is cross-linkable.

Another object of this invention is to provide said interpolymer as a stable aqueous emulsion which is readily sprayable with existing equipment.

It is a further object of this invention to provide such an interpolymer which forms clear films that resist discoloration and have a high resiliency and compressibility.

It is also a further object of this invention to provide such an interpolymer which cures rapidly and completely under the wide variety of conditions commonly used for curing such polymer films.

Other and related objects will be apparent from the following description of the invention.

The foregoing objects are achieved by this invention which comprises an aqueous latex of an interpolymer comprising a major proportion of the vinyl ester interpolymerized with polymerizable comonomers including a film-forming-temperature regulating amount of a comonomer such as an u,/3-ethylenically unsaturated nitrile or an alkyl acrylate or methacrylate, a crosslinking amount of a reactive comonomer such as an N-alkylol acrylamide which is preferably used in combination with a synergistic, polymerizable poly(ethylenically unsaturated) comonomer such as diallyl maleate and a cure-catalyzing amount of an ethylenically mono-unsaturated, monoor di-carboxylic acid. The latex is prepared by emulsion polymerization using an emulsion stabilizing amount of an anionic or a nonionic surfactant or mixture thereof.

The major monomer in the interpolymer, which comprises from about 51 to about 98 weight percent thereof, is a vinyl ester. Vinyl esters of alkanoic acids having from 1 to about 10 carbons can be used, and typical examples of these include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, Winyl isobutyrate, vinyl valerate, vinyl Z-ethyl-hexanoate, vinyl isooctanoate, vinyl nononoate, vinyl decanoate, vinyl pivalate, etc. Of the foregoing vinyl esters, vinyl acetate is the preferred monomer because of its ready availability and low cost as Well as the superior properties of polymer prepared with this ester.

The vinyl ester polymers generally form films at temperatures slightly in excess of the common ambient temperatures. The filrn forming temperature of a polymer can be determined by a conventional procedure. In this procedure, a film of the polymer, usually a latex film, is applied to a metal surface and permitted to dry. A temperature differential is established on the metal surface using a standardized procedure and the quality of the dried film is visually inspected. The temperature of the metal surface immediately above the temperature at the region Where cracks appears in the dried film is recorded as the limiting film forming temperature. A typical polyvinyl ester, polyvinyl acetate, has a film forming temperature of about 30 C. Accordingly, a film-formingtemperature regulating amount of an interpolymerizable comonomer can be used to impart the desired filming temperature to the vinyl ester interpolymer. This comonomer can be used in an amount from 1 to about 30, preferably from 5 to about 25, percent of the total polymer weight, sufficient to effect an appreciable change in the film-forming temperature of the polymer.

Examples of suitable film-forming-temperature regulating comonomers include the C to C monohydroxy alcohol esters of acrylic and methacrylic acids and C to C ethenically unsaturated nitriles. Acrylic acid esters function to reduce the film-forming-temperature of the vinyl ester interpolymer. The methacrylate esters, however, form films at more elevated temperatures, e.g., the film forming temperature of a polymethylmethacrylate is about 105 C. These comonomers, therefore, function to elevate the film-forming temperature of the vinyl ester interpolymer and can be used when it is desired to elevate the film-forming temperature of the polymer above about 30 C. or can be used with the acrylate esters when it is desired to slightly raise the film-forming temperature of the interpolymers of the vinyl ester and the acrylate esters. Examples of suitable esters include: methyl acrylate, methyl methacrylate, ethyl acrylate, isopropyl methacrylate, butyl acrylate, amyl methacrylate, 2-ethyl-hexyl acrylate, octyl methacrylate, nonyl acrylate, deeyl methacrylate, etc.

Instead of or besides the aforementioned comonomers, an alpha, beta-ethylenically unsaturated nitrile having from 3 to about 6 carbons can be used. Examples of these are acrylonitrile, methacrylonitrile, teracrylonitrile, tiglonitrile, pentenenitrile, etc. Of these, acrylonitrile is preferred for its greater availability and lower cost than the other nitriles.

The interpolymer also contains a minor quantity of an acid curable, copolymerizable, N-alkylol acrylomide or methacrylamide. The amount of this reactive cornonomer is from about 0.5 to about 5.0, preferably from about 1 to about 3, percent of the polymer weight. The nitrogen substituent can be any suitable alkylol group such as methylol, ethylol, propylol, butylol, 2-ethylhexylol, decyl- 01, etc., having from about 1 to about 10 carbons. The amide can be the amide of an ethylenically unsaturated carboxylic acid such as methacrylamide or acrylamide. Examples of suitable amides are: N-methylolacrylamide, N-ethylolacrylamide, N-isopropylolmethacrylamide, N- amylacrylamide, N-hexylolacrylamide, N-decylolacrylamide, N-2-ethylhexylolacrylamide, N-nonylolmethacrylamide, etc. The preferred reagents are N-methylolacrylamide or N-methylolmethacrylamide because of their ready availability and lower cost.

Instead of, or besides, the aforementioned N-alkylol acrylamide or methylacrylamide, there can be employed an equivalent weight amount of a cross-linking comonomer which is prepared by condensing formaldehyde with an N-3-0xohydrocarbon-substituted acrylamide. The parent compound which is used in this condensation has the following structure:

wherein R and R are hydrogen or C to about C alkyl and R is ethylene or C C alkyl substituted ethylene. These parent compounds are described in Pat. 3,377,056 and typical examples of these include N-3-oxopropylacrylamide,

N-3-oxobutylacrylamide, N-3-oxo-1-methyl-butylacrylamide, N-3-oxo-l,1-dimethyl-butylacrylamide, N-3-oxo-1-methyl-l,3-dicyclohexyl-propylacrylamide, N-3-oxol ,Z-dimethyl-l-ethylbutylacrylamide, N-3-oxo-1,5-dimethyl-1-isopropylhexylacrylamide, N-3-oxo-1,l-dibutyl-2-N-propylheptylacrylamide, N-3-oxol-methylbutyl-alpha-methylacrylamide,

etc. Formaldehyde is reacted with the parent compound under acidic conditions so as to add from 1 to 5, typically an average of about 3 formaldehyde groups per molecule and produce a hydroxymethyl derivative. The typical example of such a derivative is hydroxymethyl diacetone acrylamide which is prepared by condensing 3 formalde hyde groups with N-3-oxo-1-,1 dimethylbutyl acrylamide.

In its preferred embodiment, the interpolymer also contains a minor amount from about 0.01 to 2.0, preferably from about 0.05 to about 1.0, weight percent of a synergistic cross-linkable interpolymerizable cornonomer. These comonomers which exhibits synergism with the aforementioned cross-linking comonomers are typically non-conjugated, polyethylenically unsaturated monomers. These monomers contain the ethylenic groups in non-conjugated positions and, typically, are esters of alcohols having terminally positioned ethylenic groups and/or of carboxylic acids having ethylenic groups that are in conjugated positions with the carboxyl group. Examples of these are the monoesters of terminally mono-unsaturated, C to about C alkenols with ethylenically mono-saturated, C to about C alkenoic acids; diesters of said alkenols with C to about C alkandioic acids or the monoor diesters of said alkenols with ethylenically mono-unsaturated alkendioic acids. Other examples include the dior triesters of said alkenols with cyanuric acid as well as the diand tri-nitrogen substituted terminally unsaturated, C to about C alkenyl melamines. Other examples of cross-linking agents comprise the ditri-esters of diand tri-hydroxy C to about C alcohols with said mono-unsaturated, C to about C carboxylic acids. The following are illustrative of the useful cross-linking agents: vinyl acrylate, allyl methacrylate, butenyl vinyl acetate, vinyl tiglate, divinyl oxalate, diallyl malonate, dibutenyl succinate, divinyl adipate, etc.; vinyl fumarate, diallyl fumarate, diallyl maleate, vinyl itaconate, dibutenyl itaconate, divinyl citraconate, etc.; diallyl cyanurate, divinyl cyanurate, tributenyl cyanurate, etc.; N,N',N"-triallyl melamine, N,N'-diallyl melamine, N,N-dibutenyl melamine, etc.; ethylene diacrylate, ethylene divinylacetate, tetramethylene dimethacrylate, pentamethylene dimaleate, hexamethylene difumarate, triethylene glycol triacrylates, triethylene glycol trifumarate, triethylene glycol tritiglate, etc.

The self-curing properties are imparted to the interpolymer of this invention by the incorporation of a minor amount, e.g., from 0.05 to about 2.0, preferably from about 0.1 to about 1.0 weight percent of an ethylenically unsaturated, monoor di-carboxylic acid. Examples of suitable ethylenically unsaturated acids that can be used to impart this self-curing property include the monocarboxylic ethylenically unsaturated acids such as acrylic, vinyl acetic, tiglic, etc., as well as the dicarboxylic ethylenically unsaturated acids such as maleic, fumaric, itaconic, maleic, citraconic, hydromuconic, allylmolonic, etc. In general, these acids will have from about 3 to about 6 carbon atoms. In addition to promotion of the curing of films prepared from the latex, the acid tends to stabilize the latex emulsion.

The polymerization of the aforementioned monomers is performed by emulsion polymerization, generally under batch conditions; however, continuous processing can be employed if desired. The reactor used for the polymerization can be a jacketed kettle having stirring means with provisions to circulate a cooling medium through the jacket of the kettle to maintain the desired temperature. The aqueous medium is stirred to maintain dispersion of the monomers and the interpolymer in the aqueous medium. When necessary to achieve a stable latex, the pH of the aqueous medium can be controlled by the addition of various buffering agents. A suitable emulsifying agent of the anionic or nonionic types or combinations thereof is used in the polymerization. The amount of emulsifying agent is generally from about 0.1 to about 10, preferably from about 1 to about 5, weight percent of the monomers used in the polymerization.

A water soluble, free radical catalyst such as a water soluble peracid and salt thereof is used as the initiating catalyst and this can be used alone or in combination with an active reducing agent in a redox couple. The catalyst is used in concentration from about 0.01 to about 2, preferably from about 0.1 to about 0.5 weight percent of the monomers used in the polymerization.

If desired, the polymerization medium can also contain a minor quantity, e.g., from about 0.1 to about 5 weight percent of a protective colloid to improve the adhesiveness of the product.

With most crosslinking comonomers, it is preferred not to use any buffering agent since it raises the pH of the polymerization and of the resultant latex and tends to decrease crosslinking. With highly reactive comonomers, i.e., those which undergo an excessive amount of crosslinking during polymerization such that the latex becomes unstable and tends to coagulate, a bulfering agent can be added to reduce the degree of crosslinking which occurs during polymerization. Any suitable buffering agent can be used for this purpose. When a buffering agent is used, the pH can be maintained at a value from about 2.0 to 7.0 and most preferably from about 2.5 to 5.0 by the addition of a buffering agent. Suitable agents comprise the alkali metal or ammonium salts of weak acids, e.g., sodium carbonate, potassium bicarbonate, lithium carbonate, potassium acid phthalate, potassium citrate, sodium acetate, potassium acid phosphate, etc.

The emulsifying agent can be any of the nonionic or anionic oil-in-water surface active agents. In the following discussion of emulsifying agents, frequent reference will be made to a cloud point of a particular agent. The cloud points which are recited are based on 1 weight percent aqueous solutions of the agent. A relatively hydrophobic agent is one having a cloud point below 190 F. and a relatively hydrophilic agent is one having a cloud point of 190 F. or above.

A single emulsifying agent can be used or the emulsifying agents can be used in combination. When combinations of emulsifying agents are used, it is advantageous to use a relatively hydrophobic agent.

Suitable nonionic emulsifying agents include polyoxyethylene condensates represented by the following general formula:

where R is the residue of a fatty alcohol, acid, amide, or amine having from 10 to 18 carbon atoms or an alkyl phenol having from 10 to 18 carbon atoms; and where n is an integer of 1 or above and preferably between 5 and 30. Some specific examples of polyoxyethylene condensates which can be used include polyoxyethylene alrphatic ethers such as polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, polyoxyethylene hydroabietyl ether and the like; polyoxyethylene alkaryl ethers such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether and the like; polyoxyethylene esters of higher fatty acids such as polyoxyethylene laurate, polyoxyethylene oleate and the like as well as condensates of ethylene oxide with resin acids and tall oil acids; polyoxyethylene amide and amine condensates such as N-polyoxyethylene lauramide and N-lauryl-N-polyoxyethylene ethyl amine and the like; and polyoxyethylene thioethers such as polyoxyethylene n-dodecyl thioether.

Some examples of nonionic emulsifying agents which can be used include a polyoxyethylene nonylphenyl ether having a cloud point of between 126 and 130 F. and marketed under the trademark Igepal CO-630, and a polyoxyethylene nonylphenol ether having a cloud point above 212 F. and marketed under the trademark Igepal CO-887. A similar polyoxyethylene nonylphenyl ether having a cloud point of about 86 F. is marketed under the trademark Igepal CO-610 and is also a good emulsifying agent. Another agent is a polyoxyethylene octylphenyl ether having a cloud point of between 80 F. and 160 F. and marketed under the trademark Triton X-100. Other emulsifying agents include a polyoxyethylene oleyl ether having a cloud point of between 80 F. and 160 F. and marketed under the trademark Atlas 6-3915, and a polyoxyethylene lauryl ether having a cloud point above 190 F. and marketed under the trade mark Brij 35."

The nonionic emulsifying agents which can be used according to this invention also include a series of surface active agents known as Pluronics. The Pluronics have the general formula:

where a, b and c are integers between 1 and about 100. As the ratio of b to a and 0 increases, the compounds become less water soluble or more oil soluble and thus more hydrophobic, while as the ratio decreases the compounds become more water soluble and less oil soluble. An example of this class is Plurouic L-64 which has a cloud point of about 140 F. and a polyoxypropylene chain having a molecular weight of 1500 to 1800 and a polyoxyethylene content that is 40 to 50 percent of the total weight of the molecule. Another useful example is Pluronic F-68, a polyoxyethylene-polyoxypropylene glycol having a cloud point of about 212 F. and a polyoxyethylene content of about to percent of the total weight of the molecule.

A class of suitable emulsifying agents are a series of ethylene oxide adducts of acetylenic glycols sold commercially under the name Surfynols. This class of compounds can be represented by the formula:

in which R and R are alkyl radicals containing from 3 to 10 carbon atoms, R and R are selected from the group consisting of methyl and ethyl, and x and y are integers having a sum in the range of 3 to 60, inclusive.

Representative of the Surfynols are Surfynol 465 which is an ethylene oxide adduct of 2,4,7,9-tetramethyl decynediol containing an average of 10 moles of ethylene oxide per mole of the surface active agent. Surfynol 485 corresponds to Surfynol 465 but contains an average of 30 moles of ethylene oxide per mole of surface active agent. Surfynol 485 has a cloud point about 212 F.

Anionic emulsifying agents which can be employed herein include anionic compounds obtained by sulfonation of fatty derivatives such as sulfonated tallow, sulfonated vegetable oils and sulfonated marine animal oils. Commercially available emulsifiers of this group are Tallo san RC, a sulfonated tallow marketed by General Dyestuff Corporation; Acidolate, a sulfonated oil marketed by White Laboratories, Inc.; and Chemoil 412, a sulfonated castor oil marketed by Standard Chemical Company.

Various sulfonated and sulfated fatty acid esters of monoand polyvalent alcohols are also suitable such as Nopco 2272R, a sulfated butyl ester of a fatty ester marketed by Nopco Chemical Company; Nopco 1471, a sulfated vegetable oil marketed by Nopco Chemical Company; Sandozol N, a sulfated fatty ester marketed by Sandoz, Inc.; and Stantex 322, an ester sulfate marketed by Standard Chemical Products, Inc.

Sulfated and sulfonated fatty alcohols are also useful as an emulsifier and include anionic agents such as Duponal ME, a sodium lauryl sulfate, Duponal L142, a sodium cetyl sulfate, Duponal LS, a sodium oleyl sulfate which is marketed by E. l. duPont de Nemours and Company; and Tergitol 4, a sodium sulfate derivative of 7- ethyl-2-methyl, 4-undecanol, Tergitol 7, a sodium sulfate derivative of 3,9-diethyl tridecanol-6 and Tergitol 08, a sodium sulfate derivative of 2-ethyl-1-hexanol, which are marketed by Union Carbide Corporation, Chemical Divisron.

A particularly useful class of anionic surfactants which can be employed comprises the C to C alkyl and C to C cycloalkyl esters of alkali metal sulfoalkanedioic acids having from 3 to about 6 carbons. Examples of these include diethyl sodium sulfosuccinate, di-n-octyl potassium sulfosuccinate, dicyclohexyl lithium sulfoglutarate, di- (methylcyclopentyDsodium sulfoadipate, dicycloheptyl cesium sulfomalonate, diamyl sodium sulfoadipate, etc.

The half esterified, half ethoxylated derivatives of the aforementioned alkali metal sulfoalkanedioic acids are preferred emulsifiers. These agents have one of the carboxylic acid sites esterified with a C to C alkanol or C to C cycloalkanol and the remaining carboxylic acid site condensed with from 2 to about 20, preferably from 8 to 16 and, most preferably, from 10 to 12 ethylene oxide units per mole to add a polyethoxylol group. Examples of these are: hexyl polyethoxylol sodium sulfosuccinate, isopropyl polyethoxylol potassium sulfoglutarate, decyl polyethoxylol lithium sulfoadipate, cyclohexyl polyethoxylol cesium sulfomalonate, cycloheptyl polyethoxylol sodium sulfosuccinate, cyclooctyl polyethoxylol potassium sulfosuccinate, etc.

The polymerization is initiated by a water soluble free radical initiator such as a water soluble peracid or salt thereof, e.g,, hydrogen peroxide, sodium peroxide, lithium peroxide, peracetic acid, persulfuric acid or the ammonium and alkali metal salts thereof, e.g., ammonium persulfate, sodium peracetate, lithium persulfate, sodium persulfate, etc. A suitable concentration of the initiator is from 0.05 to 5.0 weight percent and preferably from 0.1 to 3 weight percent.

The free radical initiator can be used along and thermally decomposed to release the free radical initiating species or can be used in combination with a suitable reducing aent in a redox couple. The reducing agent is typically an oxidizable sulfur compound such as an alkali metal metabisulfites and pyrosulfites, e.g., sodium metabisulfite, potassium metabisulfite, sodium pyrosulfite, etc. A particularly preferred reducing agent is sodium or potassium formaldehyde sulfoxylate such as Formopon marketed by Rhom and Haas Company. The presence of the reducing agent in the polymerization medium achieves a release of free radicals at a lower temperature than necessary in its absence and thereby promotes formation of higher molecular weight copolymer products. The amount of reducing agent which can be employed throughout the copolymerization generally varies from about 0.1 to 3 weight percent of the amount of polymer, however, in a preferred embodiment, the reducing agent is only employed to initiate the reaction and hence is necessary only in small amounts which is generally between about 0.001 to 0.02 weight percent of polymer produced.

A protective colloid can be used to increase the adhesiveness of film prepared from the latex. The amount used can be from 0.1 to 3, preferably from 0.5 to 1.5 weight percent of the monomer weight. When the protective colloid is used, it is desirable to decrease the amount of surfactant used by an amount equivalent to the weight of the protective colloid, since the latter also aids the stability of the latex. This agent can be any of a wide range of compounds that are available for use as protective colloids, including many natural substances such as casein, natural gums, gelatins, agar, dextrin and globulin; suitably chemically modified polysaccharides such as hydrolyzed starch, hydroxyethyl cellulose, methyl cellulose carboxymethyl cellulose and synthetic colloids such as polyvinyl alcohol, alkali metal or ammonium salts of sulfonated polystyrene, water soluble interpolymers of acrylic acid and Z-ethylhexyl acrylate, copolymers of acrylamide and acrylic acid, partiallly hydrolyzed polyacrylamide having from 10 to 70 percent of its amide groups as carboxylic acid or alkali metal carboxylate groups, etc. The polyvinyl alcohols, which are prepared by hydrolysis of polyvinyl esters, typically polyvinylacetate, are preferred protective colloids and can be used with from 80 to 100 percent, preferably from about 90 to 100 percent of the ester groups hydrolyzed to hydroxyl groups.

The polymerization can be performed by batch polymerization wherein all the polymerization medium, emulsifier and comonomers are charged to the reaction vessel and the polymerization is started by thermal or redox reduction of the initiator. In a continuous process, the same material can be continuously charged to a reactor. The polymerization is performed at conventional conditions comprising temperatures from about 70 to 225 F., preferably from 120 to 175 F. and sufiicient time to achieve a low free monomer content, e.g., from 1 to about 8 hours, preferably from 3 to about 7 hours, to produce a latex having less than 3, preferably less than 1.5, weight percent free monomer.

The preferred procedure is a modified batch processing wherein the major amounts of some or all the comonomers and emulsifier are charged to the reaction vessel after polymerization has been initiated. In this manner, control over the copolymerization of monomers having widely varied degrees of reactivity can be achieved.

It is preferred to add the vinyl ester intermittently or continuously over the polymerization period. The filmforming-temperature regulating comonomers such as the acrylates, methacrylates or nitriles can be charged intermittently or continuously with the vinyl acetate or can be charged entirely to the reactor at the start of polymerization.

The methacrylamide and acrylamide derivatives that are used as the acid curable crosslinking comonomers, i.e., N-alkyl methacrylamide or acrylamide or the formaldehyde condensates of the N-3-oxohydrocarbyl acrylamides, are preferably slowly added during polymerization to avoid an excessive increase in viscosity of the latex which otherwise occurs when the entire amount of these comonomers is added to the initial charge to the polymerization vessel. The polymerizable acid catalyst is also, preferably, continuously or intermittently added during the polymeriaztion. From 40 to 100 percent of the amount of these comonomers can be added in this fashion, the balance, if any, being introduced with the initial charge.

When a synergistic crosslinking comonomer is used, its entire quantity can be added to the initial charge at the outset of polymerization. If desired, substantial amounts, e.g., from 40 to 100 percent of the total amount of this comonomer, can be intermittently or continuously added during the polymerization. Some of these comonomers such as the allyl esters are relatively less reactive and it is, therefore, preferred to add these comonomers at a sufficient rate that their addition is complete for a substantial period, e.g., about 15 minutes to about two hours, be fore addition of the last of other monomers has been completed. In this manner, accumulation of the slower reacting monomer in the latex, which may cause its coagulation, is avoided.

The emulsifier used in the polymerization can also be added, in its entirety, to the initial charge to the polymerization zone or a portion of the emulsifier, e.g., from to 25 percent thereof, can be added continuously or intermittently during polymeriaztion.

The latexes produced by this polymerization can contain from about 35 to 65 weight percent solids comprised chiefly of the interpolymers. The preferred contents of solids are from 40 to 60, and, most preferred, from 50 to about 60 weight percent. The particle size of the later is quite small, generally less than 1.0 micron and, preferably, less than about 0.5 micron.

The degree of cross-linking of films prepared from the latex can also be further improved by the addition of an extraneous acid catalyst. The films are highly cross-linkable without such catalyst, e.g., they can be cured in crosslinked films which remain from about 70 to weight percent insoluble in benzene after room temperature immersion therein for 16-18 hours. In some instances, greater solvent resistance may be desired and this can be attained by the addition of from 0.01 to 5.0, preferably from 0.1 to 1.5 weight percent of an acidic additive to the latex shortly before its application or use. Various acidic additives can be used for this purpose including inorganic acids such as sulfuric, nitric, orthophosphoric, polyphosphoric, hydrochloric, hydrofluoric acids, etc.; as well as organic C to about C alkyl and C to about C aryl sulfonic acids such as: methane, ethane, isopropane, butane, 2methylbutane, hexane sulfonic acids, etc.; benzene, ptoluene, cumene, ethylbenzene, xylene sulfonic acids, etc. Salts of these acids with fugative, i.e., volatilizable bases such as the ammonium and the C to C alkyl ammonium A jacketed autoclave of 2% gallon capacity provided with a mechanical stirrer is used in this and following examples. The autoclave is fitted with a reflux condenser, thermometer and an inlet to introduce materials during the polymerization. A steam line and a cooling water line are connected to the jacket to provide heating and cooling,

. respectively, of the contents of the autoclave.

The autoclave is charged with 2000 grams water, 213 grams Aerosol A102, a 30 weight percent aqueous solution of disodium sulfosuccinate ester of an ethylene glycol mono C -C alkyl ether, 266 grams vinyl acetate, 45 grams butyl acrylate, grams potassium persulfate and 500 grams of water to rinse the reagents into the autoclave. The autoclave is purged with nitrogen and then heated to 160 F.

The autoclave is stirred at 200 revolutions per minute and a solution of 213 grams butyl acrylate and 15.8 grams diallyl maleate in 1205 grams of vinyl acetate is slowly added during the first two hours of polymerization followed by a solution of 213 grams butyl acrylate in 1205 grams vinyl acetate during the next two hours. A solution of 105 grams N-methylolacrylamide, 15.8 grams itaconic acid and 213 grams Aerosol A102 in 350 grams water is also slowly added over the first four hours of polymerization.

The autoclave is thereafter maintained at 160 F. for one more hour and then a solution of 1.5 grams potassium persulfate in grams water is added and the polymerization continued until the residual monomer content is about 0.5 percent. The resultant latex has 50.5 percent solids, 0.9 percent residual monomer, a viscosity of 210 centipoises and a pH of 4.3. The polymer contains 14.6 percent butyl acrylate. The films prepared from the latex are highly cross-linked after curing at 270 F. for 3 minutes, about 79 percent remaining undissolved after 'l618 hours in benzene at 75 F.

When a sample of the latex is admixed with 1 weight percent of para-tolyl sulfonic acid, the resultant film after curing is highly solvent resistant, 97.4 percent remaining undissolved after 16-18 hours in benzene at 75 F.

EXAMPLE 2 The procedure of Example 1 is repeated except 315 grams of methyl methacrylate are substituted for the butyl acrylate previously described. The resultant latex contains 49.7 percent solids, 0.8 percent residual monomer, a viscosity of 140 centipoises and a pH of 4.4. The polymer contains 8.8 percent methyl methacrylate. A film of the polymer after curing for 3 minutes at 270 F. is solvent resistant, 87 percent remaining undissolved after 16-18 hours in benzene at 75 F.

EXAMPLE 3 The procedure of Example 1 is repeated with the substitution of 15.8 grams acrylic acid for the itaconic acid. The resultant latex has 49.9 percent soilds, 0.5 percent residual monomer, a viscosity of 970 centipoises and a pH of 4.9. A film of the polymer after curing for 3 minutes at 270 F. is solvent resistant, 75 percent remaining undissolved after 1618 hours in benzene at 75 F EXAMPLE 4 The procedure of Example 1 is repeated with the substit'ution of 15.8 grams methacrylic acid for the itaconic acld previously described. The resultant latex has 49.4 percent solids, 0.8 percent residual monomer, a viscosity of 550 centipoises and a pH of 5.0. A film of the latex after curing at 270 F. for 3 minutes is solvent resistant, 76 percent remaining undissolved after 16-18 hours in benzene at F.

EXAMPLE 5 The polymerization of Example 1 is repeated with the substitution of 60 grams Z-ethylhexyl acrylate for the 45 grams butyl acrylate initially added in Example 1. Solutions of: 285 grams 2-ethylhexyl acrylate, 15.8 grams diallyl maleate in 1135 grams vinyl acetate and of 285 grams 2-ethylhexyl acrylate in 1135 grams vinyl acetate are substituted for the corresponding butyl acrylate solutions used in Example 1.

The resultant latex has a total solids content of 48.2 weight percent and 0.7 weight percent residual monomer, and a viscosity of 1860 centipoises and a pH of 4.5. A film of the latex after curing at 270 F. for 3 minutes was insoluble in benzene, 89.5 weight percent remaining undissolved after 16-18 hours in benzene at 75 F.

The latexes as prepared herein have sufficient stability to insure a long shelf life. In some instances, however, stability under high shear conditions is desirable. This stability is commonly referred to as mechanical stability and is determined by placing a sample of the latex in a Waring blender operated at a high speed for up to about 15 minutes. If the latex sample remains stable after this treatment, the latex has excellent mechanical stability. Such stability can be imparted to the latexes by a post polymerization treatment. This treatment comprises adjustment of the latex pH, when necessary, to raise its value to 6.5 to 8.5, preferably to 7.0 by the addition of a volatilizable base such as ammonia, ammonium hydroxide and the C to C alkyl amines, e.g., methyl amine, trimethyl amine, amyl amine, etc., and the addition of from 0.5 to 1.5 percent of the polymer weight of an anionic surfactant. A typical preferred post treatment would comprise the addition of ammonium hydroxide to raise the latex pH to 7.0 and the addition of 1 Weight percent Aerosol MA-80, dihexyl sodium sulfosuccinate.

Viscosities reported herein are determined at 24 C.

The preceding examples are intended solely to illustrate the presently preferred mode of practice of the invntion and to demonstrate results obtainable therewith. It is not intended that the examples be construed as unduly limiting of the invention, but instead, that the invention be defined by the reagents and conditions, and their obvious equivalents, set forth in the following claims.

I claim:

1. An aqueous latex of a vinyl acetate polymer having the property of forming selfcuring films without the use of an extraneous curing additive which comprises: water; from 1 to about 10 weight percent of an anionic or nonionic surfactant or mixture thereof; and from 30 to 65 weight percent of a polymer comprising:

a major proportion of vinyl acetate interpolymerized with the following monomers:

from 1 to 30 weight percent of a comonomer which is a C to C alkanol ester of methacrylic or acrylic acid, and mixtures thereof; from 0.5 to 5.0 weight percent of an acid curable, crosslinlftiing N-C to C alkylol acrylamide or methacrylam e from 0.05 to about 2.0 weight percent of an acid catalyst comprislng an ethyleneically unsaturated aliphatic mono or dicarboxylic acid having from 3 to about 6 carbons; and

from 0.01 to about 2.0 weight percent of a cross-linkable comonomer which is a diester of a terminally unsaturated C to about C alkenol with a C to about C alkendioic acid or the dior tri-ester of said alkenol with cyanuric acid. 2. The latex of claim 1 wherein said curable crosslinking comonomer is an N-alkylolacrylamide.

3. The latex of claim 2 wherein said N-alkylolacrylamide is N-methylolacrylamide.

4. The latex of claim 2 wherein said cross-linkable comonomer is an ester of an ethylenically unsaturated alkendioic acid and a terminally unsaturated C to about C alkenol.

5. The latex of claim 4 wherein said ester is diallyl maleate.

6. The latex of claim 1 wherein said emulsifier is a nonionic emulsifier.

7. The latex of claim 6 wherein said emulsifier comprises a mixture of a condensate of from 5 to 30 ethylene oxide units with an alkylphenol of to 18 carbons and a block copolymer of polyoxypropylene and polyoxyethylene of the formula:

wherein a, b and c are integers between 1 and about 100.

8. The latex of claim 1 wherein said acid catalyst is acrylic or methacrylic acid.

9. The latex of claim 1 wherein said comonomer is butyl acrylate.

10. The latex of claim 1 wherein said comonomer is 2- ethylhexyl acrylate.

11. An aqueous latex of a vinyl acetate polymer having the property of forming self-curing films without the use of an extraneous curing additive which comprises: water, from 1 to about 10 weight percent of an anionic or nonionic surfactant or mixtures thereof; and from 30 to 65 weight percent of a polymer consisting essentially of:

from 5 to 25 weight percent of an C to C alkanol ester of methacrylic or acrylic acid or mixtures thereof;

from 0.5 to 5.0 weight percent of an N-C to C alkylol acrylamide or methacrylamide;

from 0.05 to 2.0 weight percent of an ethylenically unsaturated aliphatic monoor dicarboxylic acid having from 3 to about 6 carbons;

from 0.01 to about 2.0 weight percent of a cross-linkable comonomer which is a diester of a terminally unsaturated C to about C alkenol with a C to about C alkendioic acid or the dior triester of said alkenol with cyanuric acid; and

the balance of said polymer being vinyl acetate.

12. The latex of claim 11 wherein said alkenol ester is butyl acrylate.

13. The latex of claim 11 wherein said alkenol ester is 2-ethylhexyl acrylate.

14. The latex of claim 11 wherein said alkenol ester is methyl methacrylate.

15. The latex of claim 11 wherein said NC to C alkylol acrylamide or methacrylamide is N-methylol acrylamide.

16. The latex of claim 11 wherein said cross-linkable comonomer is diallyl maleate.

17. The latex of claim 11 having an improved stability with a pH from 6.5 to 8.5 and being prepared by the addition to the latex after its polymerization of from 0.5 to 1.5 weight percent of an anionic surfactant and a sufficient quantity of ammonia, ammonium hydroxide or a C to C alkylamine to raise the pH of said latex to said value.

18. The latex of claim 17 wherein said anionic surfactant is dihexylsodium sulfosuccinate.

19. The latex of claim 11 wherein said surfactant is disodium sulfosuccinate ester of an ethylene glycol mono- C -C alkyl ether.

References Cited UNITED STATES PATENTS 3,003,987 10/1961 Hager et al 26029.6 TA 3,081,197 3/1963 Adelman 26029.6 TA 3,258,443 6/1966 Cantor et al. 26029.6 TA 3,301,809 1/1967 Goldberg et al. 26029.6 3,345,318 10/1967 Lindemann et al. 26029.6 TA 3,380,851 4/1968 Lindemann et al. 260-29.6 TAX 3,164,562 1/1965 Breed 26029.6 TA 3,231,533 1/1966 Garrett et al. 26029.6 TA 3,256,233 6/1966 Hahn et a1 26029.6 TA 3,262,985 7/1966 Miiller et al. 26029.6 TAX 3,423,353 1/1969 Levine et al 26029.6 T

JOAN B. EVANS, Primary Examiner US. Cl. X.R.

26029.6 T, 29.6 TA, 851, 883, 885, 80.5 

